The present invention relates to a photographic lens consisting of a divergent front lens group and a convergent rear lens group, more particularly to a zoom lens capable of altering the focal length by changing the distance between the front lens group and the rear lens group.
The zoom lens of this type has long been known, while it is only quite recently that a lens with an image quality capable of being brought into practice has been realized.
In accordance with this system, the zoom lens is always of inverted telephoto arrangement regardless of the relative position of the front lens group to the rear lens group, being arranged in such a manner that the distortion which is the most remarkable of the aberrations taking place at the wide angle side, while the arrangement is not profitable for the compensation of the spherical aberration and the coma at the telephoto side. Consequently, the spherical aberration and the coma have so far been compensated only by prolonging the total length of the lens system or increasing the number of the lenses composing the system.
The U.S. Pat. No. 3,848,969 discloses a zoom lens of two lens groups, whereby the front lens group and the rear lens group respectively consist of five single lenses. Further in case of this zoom lens, the front lens group moves linearly during the zooming operation, while the rear lens group moves non-linearly for compensation operation. Further, one of the lenses in the front lens group consists of lanthanum crown glass.